Humins constitute a known material. U.S. Pat. No. 3,293,200 describes thermosetting adhesive compositions that are useful in the manufacture of plywood and contain, as essential ingredients, a water-soluble phenol-aldehyde resin and a water-insoluble, finely-divided humins material obtained from the manufacture of levulinic acid by acid hydrolysis of lignocellulose, i.e. a combination of carbohydrates and lignin. Although various procedures are known for the manufacture of levulinic acid from lignocellulose, the reaction generally is carried out under severe acid hydrolysis conditions at a temperature in excess of 150° C., usually between 170° C. and 210° C. in the presence of a strong acid catalyst. During the reaction, the humins material is formed as a result of an acid breakdown of lignocellulose while substantially the entire carbohydrate portion of the lignocellulose is degraded and the hexosans converted to the desired levulinic acid.
Humins have been obtained in the dehydration of carbohydrates in the manufacture of levulinic acid, 5-hydroxymethylfurfural and/or 5-alkoxymethylfurfural and/or acyloxymethyl-furfural. An example of such a dehydration reaction is described in DE 3621517. Other examples of such a process are described in WO 2007/104514 describing the preparation of alkoxymethylfurfural, and WO 2007/104515, disclosing the preparation of acyloxymethyl-furfural. Although the latter processes have set out to reduce the yield of humins, the processes unavoidably yield amounts of humins for which a useful outlet is sought.
An application of humins has been described in DE 3612517, where it is stated that the humins, i.e. the by-product of the preparation of alkoxymethylfurfural and alkyl levulinates from cellulose, lignocellulose or starch with an alcohol, can only be used for the provision of heat by combusting it. In a journal article by Robert-Jan van Putten et al., Chem. Rev., 2013, 113(3), 1499-1597, the formation of humins from the dehydration of carbohydrates is discussed. The article mentions the forming of humins as unwanted by-product in addition to the formation of the desired products hydroxymethyl furfural, furfural and levulinic acid. It is mentioned that the most likely applications for humins are either as a fuel, particularly for generating heat for the various operations to accomplish the carbohydrate dehydration, or as compost.
It would therefore be very advantageous, if humins can be used in a more economic and value-added application. In WO2015088341 a composition is disclosed wherein furfuryl alcohol and humins are used as wood adhesive and impregnating agent for wood and other materials.